Lipid Composition in Rabbit Sarcoplasmic Reticulum and Occurrence of Alkyl Ether Phospholipids

Abstract

1. The lipids of rabbit sarcoplasmic reticulum were isolated, and the contents of individual classes of phospholipids and neutral lipids were estimated. Total lipids represented 44.5% of lyophilized sarcoplasmic reticulum and 88.8% of them were occupied by phospholipids. 2. In the phospholipids, choline-phosphoglyceride fraction was predominant (70.8%), followed by ethanolamine-phosphoglyceride fraction (16.5%), sphingomyelin (6.2%), phosphatidylinositol (2.3%)and phosphatidylserine (1.7%). The neutral lipid fraction contained cholesterol (45.5%), triglycerides (26.4%), cholesterol esters (16.2%) and free fatty acids (11.6%). 3. Choline- and ethanolamine-phosphoglyceride fractions were analyzed further by stepwise hydrolyses according to the method of Dawson. Choline-phosphoglyceride fraction contained l-0-alkyl-2-acyl-glycero-3-phosphorylcholine (8.4%) and plasmalogen (9.5%) besides diacyl analogue, whereas ethanolamine-phosphoglyceride fraction involved alkyl acyl analogue (6.4%) and plasmalogen (69.3%). These figures were confirmed by estimation of alkyl acyl and diacyl glycerol in the products of phos-pholipase C [EC 3.1.4.3]-hydrolysis after removal of plasmalogens from both fractions. Periodate oxidation and gas chromatography were also performed for the analysis of alkyl glyceryl ethers.